Besides for the ovious of the length difference, the 312 is a single step hull, and the 292 is a twin step
The 312 comes with twin Big Blocks, and the 292 comes with twin SB's.
Cockpits are about the same size. Cabin on the 312 is bigger.
My understanding has always been that unless the 312 has 454 mags or 502 mags, thats it is "slow"
Either one is going to be a great boat. Formula doesn't build the fastest boat, but they build boats that last.